Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2005
Publication Date: 6/1/2006
Citation: Davidson, R.M., Hanson, L.E., Franc, G.D., Panella, L.W. 2006. Analysis of beta-tubulin gene mutations in Cercospora beticola varying in sensitivity to benzimidazole fungicides. Journal of Phytopathology. 154:321-328. 2006. Interpretive Summary: Cercospora leaf spot, caused by the fungus Cercospora beticola is a major foliar disease of sugar beet. Fungicide sprays have been used to manage the disease. Resistance to one class of fungicides, the benzimidazoles, has been observed in the fungus, but the genetics of this resistance is not known. We tested C. beticola isolates for sensitivity to fungicide and mutations in a gene shown in other fungi to cause resistance to this fungicide class. A single mutation was found in all fungicide-tolerant isolates, and not in fungicide-sensitive isolates. In other fungi, this mutation causes sensitivity to a different class of fungicides. Isolates with this mutation showed the predicted sensitivity to an n-phenylcarbamate fungicide. Only this single mutation was found in fungi isolated from different regions of the United States in different years.
Technical Abstract: Cercospora leaf spot of sugar beet, caused by the fungus Cercospora beticola, is a major foliar pathogen on sugar beet. Fungicide sprays have been used extensively to manage Cercospora leaf spot, including the benzimidazole fungicides. Resistance to benzimidazoles has been observed in isolates of C. beticola. The precise genetic control of this resistance is not known in this fungus. We tested benzimidazole-tolerant and benzimidazole-sensitive isolates and found a single mutation in the '-tubulin gene of benzimidazole-tolerant isolates that corresponds to a mutation known to confer benzimidazole-tolerance in other ascomycetes. This mutation is predicted to cause a change from glutamic acid to alanine in the protein product. Isolates containing this mutation further show an increased sensitivity to an N-phenylcarbamate, as would be predicted based on the mutant phenotype found in other filamentous fungi. Only a single mutation was found in isolates from different regions of the United States, isolated in different growing seasons.